A photocell is illuminated by a small bright source placed 1 m away. When the same source of light is placed (1/2) m away, the number of electrons emitted by photocathode would

Option 1)

decrease by a factor of 2

Option 2)

increase by a factor of 2

Option 3)

decrease by a factor of 4

Option 4)

increase by a factor of 4

Answers (1)

As we learnt in

Effect of intensity on photoelectric current -

For a fixed frequency, the photolelectric current increases linearly with increase in intensity of light

 

 

- wherein

 

 Since Intensity (I)\alpha\frac{1}{r^{2}}

When distance become half intensity becomes 4 times

Hence number of electrons increases by factor of 4.

Correct answer is 4.


Option 1)

decrease by a factor of 2

This is an incorrect option.

Option 2)

increase by a factor of 2

This is an incorrect option.

Option 3)

decrease by a factor of 4

This is an incorrect option.

Option 4)

increase by a factor of 4

This is the correct option.

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